The present invention relates to an ink-dot printer which comprises: a magnetic ink storage means storing magnetic ink; a pair of pole plates facing each other so as to define a slit, one end portion of which is contacted with the magnetic ink supplied from the magnetic ink storage means; a magnetic field generating means for magnetizing the pole plates, thereby feeding the magnetic ink from the magnetic ink storage means into the slit to form a magnetic ink curtain in the slit; and a plurality of needles arranged adjacent to one another along the longitudinal direction of the slit and adapted selectively to move in the longitudinal direction of each needle between a first position where one end portion of each needle is immersed in the magnetic ink curtain in the slit between the pole plates and a second position where the one end portion is projected from the magnetic ink curtain in the slit, and wherein the needles are selectively moved from the first position to the second position so that the end faces of the one end portions of the needles are brought into contact with a recording sheet as a recording section, thereby forming a set of magnetic ink-dots thereon which are used to print a symbol such as a character, figure, etc.
Wire-dot printers and thermal printers are currently used. In the wire-dot printers, a plurality of needles are selectively driven so that the end faces of the distal end portions of the needles are caused to strike directly against pressure-sensitive manifold paper on a platen or to strike indirectly against recording paper on the platen through a printing ribbon, thereby forming a set of dots on the pressure-sensitive manifold paper or recording paper. The resulting set of dots constitutes a print which represents a symbol such as a character or figure. In the prior art wire-dot printers with this arrangement, however, the printing of symbols on the pressure-sensitive manifold paper or recording paper produces a lot of noise. Moreover, these printers only permit the use of pressure-sensitive manifold paper, and require expensive printing ribbons which must be frequently replaced.
In order to eliminate the drawbacks of the prior art wire-dot printers, there are proposed various ink-dot printers adopting a system in which magnetic ink is applied to the distal end portions of a plurality of needles. The needles are selectively driven so that the magnetic ink on the end faces of the distal end portions of the driven needles is transferred to a recording sheet on a platen. In these currently proposed ink-dot printers, however, when two adjacent needles are simultaneously driven to form dots on the recording sheet, the magnetic ink is often held between the distal end portions of the two needles by the action of surface tension. Magnetic ink between the distal end portions of the needles can sometimes stick to the recording sheet in bulk when magnetic ink on the end faces of the distal end portions is transferred to the recording sheet, forming spots large enough to blur print.
In forming a number of dots by repeatedly driving a single needle, in the presently proposed ink-dot printers, the drive of the needle will have to be repeated before the magnetic ink can fully be attached to the end face of the needle. Therefore, the amount of magnetic ink on the end face of the distal end portion will gradually be reduced, so that dots printed later will be faded possibly resulting in a blurry print.